Lysophosphatidic acid (LPA) is a prominent bioactive lipid component of oxidized low density lipoprotein (LDL) and is produced by activated platelets. LPA accumulates at high levels in human atherosclerotic lesions and induces vascular smooth muscle cell (SMC) proliferation and migration and vascular neointimal formation. Thus, LPA is being recognized as a risk factor for atherosclerosis. However, the molecular mechanism by which LPA contributes to atherogenesis is unclear. In an effort to identify novel pathogenic mediators of LPA, our gene microarray assays revealed that LPA induced the expression of a group of proteins, including IL-6, IL- 8, Tuftelin and Cyr61, that have been implicated in SMC proliferation and migration. Our data further demonstrated that the Cyr61-specific antibody, but not the others, almost completely blocked LPA-induced SMC migration. Importantly, we observed that LPA stimulates Cyr61 expression in vascular neointimal lesions. These data strongly support a novel role of Cyr61 in LPA-induced vascular neointimal formation. To this end, our study has revealed that 1) antibodies against Cyr61 and particular integrins blocked LPA-induced SMC migration; 2) LPA induced activation of a series of protein kinases including PKD, MAPK, and novel tyrosine kinases, JAK2, Lyn and Txk; 4) knockout of LPA receptor 1 blocked LPA activation of these kinases; and 5) LPA-induced Cyr61 expression and SMC proliferation and migration were not inhibited by PPAR3 antagonist. Based on these novel findings, we hypothesize that LPA, via its specific cell surface receptor(s), activates a specific intracellular signaling pathway, leading to de novo expression of Cyr61, which, in turn activates the integrin pathway leading to SMC proliferation/migration and vascular neointimal formation. Aim 1: Identify LPA- triggered novel intracellular pathways leading to matricellular Cyr61 expression. Aim 2: Determine the specific LPA receptors and the roles of Cyr61 and integrins in LPA-induced SMC cellular response using novel LPA receptor-knockout cells and siRNA approaches. Aim 3: Determine whether genetic depletion of LPA receptors diminishes LPA-induced Cyr61production and neointimal formation, and determine the novel roles of Cyr61 and specific integrins in LPA-induced vascular wall remodeling using novel LPA receptor knockout mouse models and the unique siRNA approach. To date, the specific cell surface receptor that mediates LPA-induced Cyr61 expression is unknown. The molecular cascades that mediate LPA-induced Cyr61 expression in the vascular wall cells have never been investigated. More importantly, whether and how Cyr61 mediates LPA- induced SMC proliferation/migration and vascular remodeling is completely unknown. Thus, the proposed study will determine a novel convergence mechanism by which the LPA/GPCR pathway and the integrin pathway are interconnected by Cyr61 and mediate LPA-induced vascular wall remodeling. The information obtained from the proposed studies will lead to a new breakthrough in understanding the mechanism by which bioactive lipid LPA and oxidized LDL contribute to vascular neointimal formation and atherogenesis.